fix promo #3

app/services/promo.py

@@ -9,6 +9,16 @@ promo_codes = db["promo_codes"]
 promo_redemptions = db["promo_redemptions"]
 
 class PromoService:
+    
+    @staticmethod
+    def _to_json(doc: dict | None):
+        if not doc:
+            return doc
+        doc = dict(doc)
+        if "_id" in doc:
+            doc["_id"] = str(doc["_id"])
+        return doc
+    
     def __init__(self):
         self.coins = CoinsService()
 
@@ -42,11 +52,12 @@ class PromoService:
             # можно точнее ловить DuplicateKeyError
             raise HTTPException(status_code=409, detail="Promo code already exists")
         doc["_id"] = r.inserted_id
-        return doc
+        return self._to_json(doc)
 
     async def list(self, limit: int = 50, skip: int = 0):
         cursor = promo_codes.find({}).sort("created_at", -1).skip(skip).limit(limit)
-        return await cursor.to_list(length=limit)
+        items = await cursor.to_list(length=limit)
+        return [self._to_json(x) for x in items]
 
     async def update(self, promo_id: str, payload):
         try:
@@ -59,7 +70,7 @@ class PromoService:
             doc = await promo_codes.find_one({"_id": oid})
             if not doc:
                 raise HTTPException(status_code=404, detail="Promo not found")
-            return doc
+            return self._to_json(doc)
 
         update_data["updated_at"] = datetime.utcnow()
 
@@ -70,7 +81,7 @@ class PromoService:
         )
         if not doc:
             raise HTTPException(status_code=404, detail="Promo not found")
-        return doc
+        return self._to_json(doc)
 
     async def delete(self, promo_id: str):
         try: